An ink-jet printer is a type of non-impact printer which forms characters and other images by controllably spraying drops of ink from a print head. One conventional type of ink-jet print head consists of a replaceable cartridge or pen which is removably mounted to a movable carriage. The pen controllably ejects liquid ink through multiple nozzles in the form of drops that travel across a small air gap and land on a recording media.
Ink droplets are ejected from individual nozzles by localized heating. A small heating element, typically in the form of a thermal resistor, is disposed at each nozzle. An electrical current is passed through the element to heat it up. The heated element vaporizes a tiny volume of ink, which is ejected through the nozzle. The heating elements are commonly formed on a single silicon wafer chip, which make the replaceable pen easy to assemble and inexpensive to produce.
Current print head technology also implements firing logic on the print head. The firing logic is formed into the silicon wafer that forms the nozzles and heated firing elements. This reduces the number of connections to the pen and allows the print head to decode data at least partially on the fly. Logic-based pens are relatively inexpensive to produce as the logic circuitry is incorporated into the same silicon chip that is used to hold the heating resistors.
A problem encountered in such print heads concerns destructive overheating of the firing resistors (or other circuit components) as a result of power supply surges or interruptions. It would be desirable to protect these circuit elements from interruptions to avoid the destructive overheating. Any solution, however, must be relatively inexpensive because the pens are designed to be replaceable and/or disposable to satisfy other manufacturing goals of providing an efficient way to replenish spent ink supplies.
Accordingly, there is a need for a replaceable inkjet print head that protects the logic circuitry (namely, the firing resistors) against power supply interruptions, without increasing the manufacturing cost of replaceable pens.